As information technologies develop, complexity of an optical communications network constantly increases. A large quantity of wavelength division multiplexing (WDM) beams from different dimensions (directions/lines) need to be switched to different dimensions (that is, inter-dimension switching) on a common optical network node (for example, a backbone node in a metropolitan area network) of a plurality of tangent ring networks. In addition, the optical network node has optical add and optical drop lines connected to a convergence layer. The optical add line is used to switch, to a target dimension, a beam converged from a lower layer to the optical network node. The optical drop line is used to switch, to the optical network node, a beam that is in another dimension and that needs to be used for communication with the optical network node. Currently, network traffic keeps increasing, an optical network node has increasingly more throughputs, and one optical network node needs to process local optical add/drop services while processing beam switching in more dimensions.
In the prior art, operators may use a reconfigurable optical add/drop multiplexer (ROADM) on an optical network node to perform dimension switching, optical add or optical drop services, and the like. Currently, there are ROADMs of a plurality of structures, for implementing cross-connections and connections between optical network nodes. For example, there is an N×M ROADM, and the N×M ROADM includes M input ports, N output ports, and two levels of switch arrays. The M input ports are configured to input WDM beams, and a first-level switch array includes MXK (M rows and K columns) switch units, configured to perform optical path processing on sub-beams of the WDM beams, so that the processed sub-beams are transmitted to switch units in a second-level switch array. The second-level switch array includes N switch units arranged in a two-dimensional manner, and the switch units are configured to output, to the N output ports, the sub-beams processed by the first-level switch array. Because the switch units in the second-level switch array are arranged in a two-dimensional manner, the N×M ROADM can implement more output ports. However, because a configured structure and an optical path design are limited, the N×M ROADM can implement only an optical drop function. If both an optical add/drop function and an inter-dimension switching function need to be implemented, the N×M ROADM needs to be combined with another optical component. Therefore, requirements such as a high integration level, a high cross-connection capability, and low costs of an optical network cannot be met in terms of a scale, a volume, and costs.
An ROADM that can not only implement high-level integration, but also improve an cross-connection capability of an optical network node is urgently needed.